The apparatus and method of this invention concerns the production of chopped glass strand mats, particularly multilayer strand mats.
In the production of multilayer strand mats, it has been a particularly difficult problem to obtain an even distribution of the chopped glass strands in the mat. The strands may be produced in the conventional manner, such as disclosed in U.S. Pat. No. 2,719,336, assigned to the Assignee of the instant application and incorporated herein by reference. In the disclosed method, a plurality of glass strands are received in the choppers from a creel, air flow directs the streams of glass fibers in the hood and the fibers are continuously collected in the form of a mat on a foraminous conveyor chain.
The difficulty has been to provide an even distribution of the glass fibers on the conveyor because of two problems. First, the circulation of gases within the hood is difficult to control. The gas flow is generally turbulent away from the side walls of the hood and is laminar to quiescent at the side walls. In a conventional hood, more than one air inlet port may be utilized to direct the fibers in the desired patterns, however this has not solved the problem. The second problem apparently involves pressure differentials at the conveyor and immediately above the conveyor. These pressure differences cause the fibers to move or jump after deposition on the conveyor, toward low pressure areas generally adjacent the edges of the conveyor. Even if it were then possible to evenly distribute the chopped fibers on the conveyor initially, the distribution would be changed before the mat leaves the hood.